A processing plant for processing plastics material is known from DE 102 00 192 A1, in which a start-up valve is provided for the start-up. The plastics material to be processed is melted in a screw machine and firstly discharged by means of the start-up valve at the beginning of the start-up process. The discharged plastics material arrives in a cooling basin filled with water, where it can cool down and then be disposed of. At the end of the start-up process, the start-up valve is switched over, so that the molten plastics material is no longer discharged, but arrives in a downstream discharge device. A discharge device of this type is generally a granulating device, which produces a plastics material granulate from the molten plastics material. The start-up known from the prior art by means of a start-up valve is disadvantageous as the plastics material discharged during the start-up process has to be laboriously disposed of and is also a substantial safety risk because of the high temperature.
An underwater pelletizer is known from U.S. Pat. No. 4,759,889 A, in which the control valve for the granulating water is activated via a timer depending on a signal of the extruder motor. As a backup the control valve is additionally and directly activated by a pressure transducer, which is located in the extrusion chamber. The known pelletizer is difficult to start up.